Methods of the kind indicated in the introduction have been described in the patent specifications WO 88/01534, GB 218 974 and CA 1 144 873.
Activated carbon is generally used as an adsorbent. In connection with the regeneration of the active carbon the temperature is increased, whereby e.g. volatile solvents are volatilized. The heating can be carried out directly by means of steam injection or indirectly, in which case the heating medium does not get in touch with the adsorbent.
In connection with the volatilization by means of a stripping gas the temperature of the adsorbent does not need to reach the boiling point of the solvent due to the fact that the stripping gas reduces the partial pressure of the solvent. The volatilized solvent is separated in a condenser.
When using steam for direct heating and also using steam as a stripping gas, the condensed solvent is, however, to a high degree diluted in water. This inconvenience does not occur, if heating is carried out indirectly and if a not condensable gas as e.g. air or nitrogen is used. In this case energy consumption is also reduced due to the fact that the heat of vaporization is considerable and that there is no need to take care of more or less poluted waste water. New laws and regulations have given rise to increased demands regarding the purification of exhaust air carrying solvents as well as on the efficiency of equipment for gas purification. From the point of view of environment as well as from an economical point of view it is thus important that apparatuses and devices for purification can be made small, economical and efficient. It has also become evident that the purification of gases can be of interest and at least less expensive if the purification process is used for recovering e.g. expensive solvents.